﻿#region File and License Information
/*
<File>
	<License Type="BSD">
		Copyright © 2009 - 2012, Outcoder. All rights reserved.
	
		This file is part of Calcium (http://calciumsdk.net).

		Redistribution and use in source and binary forms, with or without
		modification, are permitted provided that the following conditions are met:
			* Redistributions of source code must retain the above copyright
			  notice, this list of conditions and the following disclaimer.
			* Redistributions in binary form must reproduce the above copyright
			  notice, this list of conditions and the following disclaimer in the
			  documentation and/or other materials provided with the distribution.
			* Neither the name of the <organization> nor the
			  names of its contributors may be used to endorse or promote products
			  derived from this software without specific prior written permission.

		THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
		ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
		WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
		DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> BE LIABLE FOR ANY
		DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
		(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
		LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
		ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
		(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
		SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	</License>
	<Owner Name="Daniel Vaughan" Email="danielvaughan@outcoder.com" />
	<CreationDate>2012-07-21 09:42:07Z</CreationDate>
</File>
*/
#endregion

using System.Collections.Generic;
using System.ComponentModel;

namespace Outcoder.ComponentModel
{
	/// <summary>
	/// This class is analagous to the Knockout JS style observables. 
	/// It is used to wrap a value and provides change notification for bindings 
	/// without adding plumbing to a viewmodel.
	/// <see cref="http://danielvaughan.org/post/Knockout-Style-Observables-in-XAML.aspx" />
	/// </summary>
	/// <example>
	/// class MainWindowViewModel
	///{
	///    readonly ObservableValue&lt;string&gt; firstName = new ObservableValue&lt;string&gt;("Alan");
	///
	///    public ObservableValue&lt;string&gt; FirstName
	///    {
	///        get
	///        {
	///           return firstName;
	///        }
	///    }
	/// ...
	/// }
	/// Bind to the value in XAML using:
	/// &lt;TextBox Text="{Binding Path=FirstName.Value, UpdateSourceTrigger=PropertyChanged}" /&gt;
	/// </example>
	/// <typeparam name="T">The type of field that is managed by this object.</typeparam>
	public class ObservableValue<T> : INotifyPropertyChanged
	{
		T valueField;

		/// <summary>
		/// Gets or sets the value that is wrapped by this object.
		/// </summary>
		/// <value>
		/// The value.
		/// </value>
		public T Value
		{
			get
			{
				return valueField;
			}
			set
			{
				if (!EqualityComparer<T>.Default.Equals(valueField, value))
				{
					valueField = value;
					OnPropertyChanged("Value");
				}
			}
		}

		/// <summary>
		/// Initializes a new instance of the <see cref="ObservableValue&lt;T&gt;"/> class.
		/// </summary>
		/// <param name="value">The value.</param>
		public ObservableValue(T value = default(T))
		{
			Value = value;
		}

		/// <summary>
		/// Occurs when the <seealso cref="Value"/> property changes.
		/// </summary>
		public event PropertyChangedEventHandler PropertyChanged;

		void OnPropertyChanged(string propertyName)
		{
			PropertyChangedEventHandler handler = PropertyChanged;
			if (handler != null)
			{
				handler(this, new PropertyChangedEventArgs(propertyName));
			}
		}
	}
}
